Trajectory Tracking Of Driverless Vehicles Considering Stability

With the development of vehicular technology,the driverless cars of L4 or even L5 class have become the trend of the future.Driverless driving is different from traditional driving.Driverless driving is different from traditional driving,Starting from L3,vehicles gradually have their own "thought",and L4 and L5 driverless vehicles have their own perception,decision-making,planning,and execution.Vehicle stability can be expressed in two aspects: attitude and tire.There have been many studies on considering stability from attitude.The traditional ESC controller is an active safety controller that belongs to attitude tracking.As an important part of the vehicle’s active safety system,Electronic stability control(ESC)ensures vehicle stability through real-time monitoring and control attitude,but lacks the predictive function.When the vehicle is driving at high speed,it is difficult for the vehicle to provide stable control in a timely manner against sudden conditions.The reference trajectory of a driverless vehicle can be composed of two variables: the speed of the vehicle and the steer angle.driverless researchers have been focusing on how to track the trajectory by controlling the steer angle of the front wheel,who don’t care about the limit velocity that ensure the stability of vehicle.Lacking of vehicle stability analysis and verification on the premise of ensuring vehicle when tracking expected trajectory performance.When analyzing stability of vehicle from tire perspective,we required the slip angle of tire need stay in a stable range to protect driver safe.The main work and contributions of this study are as follows:1.The linear tire formula and the magic tire formula are used to derive the lateral force of the vehicle.An upper speed planner and front wheel angle planner are designed.After analysis,the speed and front wheel angle area can be divided into a stable area,an unstable area and a uncertain stable area.The curvature constraint of trajectory planning is derived through the formula.2.According to the hierarchical control strategy,through the established three-degree-of-freedom model,the controller is designed from the horizontal and vertical sides to control the vehicle speed and front wheel angle to achieve the purpose of tracking the trajectory.The longitudinal control of the system uses the closed loop PID algorithm of speed and lateral displacement feedback to control the throttle opening and brake pedal opening to control the speed.The lateral control of the system adopts an incremental model predictive control algorithm(MPC)with constraints to control the front angle of the vehicle.3.Joint simulations were carried out on Carsim and Simulink platforms.The simulation verified the true validity of the speed feasible domain and the front wheel corner feasible domain,and verified the effectiveness of the designed trajectory tracking algorithm.